• Sinéad Holden, Christian Lund Straszek, Michael Skovdal Rathleff, Kristian Kjær Petersen, Ewa M Roos, and Thomas Graven-Nielsen.
• SMI, Department of Health Science and Technology, Faculty of Medicine, Aalborg University, Aalborg, Denmark.
• Pain. 2018 Dec 1; 159 (12): 2530-2537.

AbstractPatellofemoral pain (PFP) is a common and recurrent knee condition in young females, characterized by pressure hyperalgesia and reduced pain inhibitory control. This study investigated antinociceptive and pronociceptive profiles in young females with long-standing (>5 years) PFP (current-PFP), those who recovered from adolescent PFP (recovered-PFP), and pain-free controls. This preregistered, assessor-blinded, cross-sectional study included 87 females younger than 25 years: 36 current-PFP, 22 recovered-PFP, and 29 pain-free controls. The primary outcome was conditioned pain modulation (CPM) assessed by increase of cuff pain thresholds during painful cuff conditioning on the contralateral leg. Secondary outcomes included pressure pain thresholds at the knee, shin, and forearm, and temporal summation of pain, assessed by pain intensity recordings on a visual analogue scale during repeated cuff pressure pain stimulations on the leg. Compared with the recovered-PFP, the current-PFP had impaired CPM (mean difference: 11.6%; P = 0.004) and reduced pressure pain thresholds at the knee, shin, and forearm which were also reduced compared to current-PFP (mean difference: 85-225 kPa; P < 0.05). There were no differences between current-PFP and controls in CPM. Current-PFP and recovered-PFP demonstrated facilitated temporal summation of pain, compared to controls (mean difference: 0.7-0.8 visual analogue scale change; P < 0.05). Compared with controls, the recovered-PFP also had reduced pressure pain thresholds at the knee, which were higher than the current-PFP (mean difference: 110-225 kPa; P < 0.05). In conclusion, both current-PFP and recovered-PFP displayed altered pain mechanisms compared to controls with no history of knee pain, despite resolution of symptoms in the recovered-PFP group. The implications of these findings in the recurrent nature of PFP requires further studies.

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